Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment, so that the sides hang off (this will make it easier to pull the cake out later) and grease lightly with cooking spray, set aside.

In a large bowl, whisk together the flour, baking powder, baking soda and salt; set aside. In a separate bowl, cream together the butter and sugar until light and fluffy, about 3 minutes. Add in the eggs, one at a time, making sure to beat the mixture well after each addition. Stir in the vanilla extract and sour cream. Add the dry ingredients, alternating with the buttermilk, starting and ending with dry. Mix until just combined after each addition. Use a rubber spatula to scrape the sides and bottom of the bowl to ensure the batter is evenly combined.

Pour the batter into the prepared baking pan and spread into an even layer. Dollop the nutella on top and use a skewer or knife to swirls it around. Sprinkle with the slivered almonds and chocolate chips and bake until golden brown and a toothpick inserted in the middle, comes out clean, about 35 to 40 minutes. Remove from the oven and let cool completely. Use the parchment paper overhang to lift the cake out of the pan. Dust with powdered sugar and cut into small squares. Enjoy right away or wrap in plastic wrap. Can be kept at room temperature for up to 3 days. Enjoy!